1. Field of the Invention
The present invention relates to a method of forming an organic polymer thin film and an apparatus for forming the organic polymer thin film. More particularly, the present invention relates to a method of advantageously forming a thin film of an organic polymer on a surface of a substrate by vacuum deposition polymerization, and an apparatus for effectively performing the method of forming a thin film of an organic polymer.
2. Description Of Related Art
Conventionally, as one kind of methods for forming an organic polymer thin film (synthetic resin thin film), there is known a vacuum deposition polymerization. In this polymerization, a plurality of kinds of monomers (raw materials) are evaporated in vacuum and polymerized on a surface of a substrate, thereby forming an organic polymer thin film on the surface of the substrate (see, JP-A-61-78463, for example).
In the above method of forming an organic polymer thin film by vacuum deposition polymerization, a special apparatus for the method is generally used. The apparatus for forming an organic polymer thin film generally includes a deposition chamber in which a substrate is disposed, and a plurality of evaporation source containers. Each of the evaporation source containers contains a separate kind of monomer and introduces the monomer into the deposition chamber by evaporating the monomer under vacuum pressure. In the apparatus, the monomers introduced into the deposition chamber in a vacuum state after being evaporated in respective evaporation source containers are polymerized on a surface of the substrate disposed in the deposition chamber. Therefore, an organic polymer thin film formed of the polymer of the monomers can be formed on the surface of the substrate.
As the conventional apparatus for forming an organic polymer thin film, there is known a batch type apparatus in which the above vacuum deposition polymerization is repeatedly operated in the same deposition chamber, thereby forming an organic polymer thin film on a surface of a plurality of substrates, which is provided in the deposition chamber one after another. Further, there is known a continuous type apparatus in which the vacuum deposition polymerization is continuously operated while a substrate is unwound from a roll of the substrate which is disposed in a deposition chamber, thereby forming an organic polymer thin film on a surface of the substrate unwound from the roll.
When an organic polymer thin film, such as a polyimide film, an aromatic polyurea film or an aromatic polyamide film, which is formed of a combination of high reactive (small activation energy for the reaction) monomers, is formed on a surface of a substrate, a monomer proportion on the surface of the substrate can be stoichiometric proportion only by opening and closing a shutter which is conventionally used for a vacuum disposition and provided between each evaporation source container and a substrate in a deposition chamber. Accordingly, the organic polymer thin film formed on the surface of the substrate can have a desired composition, and a thickness of the film can be easily controlled. As a result, when a combination of high reactive monomers is used, an organic polymer thin film can be always stably formed on a surface of a substrate with a constant composition and thickness both in the vacuum deposition polymerization operated repeatedly by using a batch-type apparatus and in the vacuum deposition polymerization operated continuously by using a continuous type apparatus.
On the other hand, in the formation of an organic polymer thin film, such as an aliphatic polyurea film, an aliphatic polyamide film, a polyester film or a polyurethane film, which is formed of a combination of low reactive (big activation energy for the reaction) monomers, a monomer proportion on the surface of the substrate cannot be easily to be stoichiometric proportion by only opening and closing the shutter. Accordingly, it is difficult to control the composition and thickness of the organic polymer thin film that is obtained by a combination of low reactive monomers. Therefore, it is extremely difficult to form an organic polymer thin film on a surface of a substrate with excellent reproducibility or repeatability both in a vacuum deposition polymerization operated repeatedly by using a batch-type apparatus and in a vacuum deposition polymerization operated continuously by using a continuous type apparatus.
Under such situation, JP-A-5-171415 discloses an apparatus for forming an organic polymer thin film in which each of evaporation source containers arranged in a deposition chamber includes an open/close device at an opening portion thereof and a vacuum exhaust device. JP-A-5-171415 further discloses that, by using the apparatus, the amount of evaporated monomer released from each evaporation source container can be separately controlled, and degree of vacuum in each evaporation source container at the time of closing the open/close device can be made equal with the degree of the vacuum during the film formation (deposition), thereby performing film formation with excellent reproducibility and stability. However, there is no difference in pressure in the evaporation source containers and in the deposition chamber of such apparatus. Accordingly, evaporation amount of each monomer is inevitably small and a speed of film formation (amount of film formation per unit time) is reduced, which results in a problem of reduction in film formation efficiency.
Further, JP-A-7-26023 discloses an apparatus that is adapted to pass carrier gas through respective evaporation source containers and introduce the carrier gas including the evaporated monomer into a deposition chamber. JP-A-7-26023 further discloses that, by adjustment of flow rate of carrier gas, introduction amount of each monomer into the deposition chamber can be controlled with high degree of accuracy, so that each monomer can be introduced into the deposition chamber so as to be stoichiometric proportion. However, in such an apparatus, the monomer is introduced into the deposition chamber with carrier gas, so that, compared to the case in which only the monomer is introduced into the deposition chamber, an amount of the monomer in the deposition chamber is inevitably made smaller. As a result, in such an apparatus, defects such as reduction in film formation efficiency cannot be avoided.
Furthermore, JP-A-2002-275619 discloses an apparatus including a pulse valve in each evaporation source container, which can be opened and closed at arbitrary time intervals. JP-A-2002-275619 further discloses that, by using the apparatus, introduction time of each monomer into the deposition chamber can be suitably determined, so that the amount of each monomer introduced into the deposition chamber can be separately controlled. However, in such an apparatus, evaporation amount of the monomers per unit time is changed by reduction in the amount of monomer in each evaporation source container, so that open/close cycle of the open/close device should be changed depending on the change of the evaporation amount of the monomer. In addition, the changes of controlling condition largely affect a thickness and reproducibility of quality of an organic polymer thin film obtained by a combination of the low reactive monomers, so that, in this conventional apparatus, it was extremely difficult to always obtain an organic polymer thin film having a constant composition and thickness, with excellent reproducibility.